Molecular mechanisms of mitochondrial diabetes (MIDD)

Mitochondria provide cells with most of the energy in the form of adenosine triphosphate (ATP). Mitochondria are complex organelles encoded both by nuclear and mtDNA. Only a few mitochondrial components are encoded by mtDNA, most of the mt-proteins are nuclear DNA encoded. Remarkably, the majority of the known mutations leading to a mitochondrial disease have been identified in mtDNA rather than in nuclear DNA. In general, the idea is that these pathogenic mutations in mtDNA affect energy supply leading to a disease state. Remarkably, different mtDNA mutations can associate with distinct disease states, a situation that is difficult to reconcile with the idea that a reduced ATP production is the sole pathogenic factor. This review deals with emerging insight into the mechanism by which the A3243G mutation in the mitochondrial tRNA (Leu, UUR) gene associates with diabetes as major clinical expression. A decrease in glucose-induced insulin secretion by pancreatic beta-cells and a premature aging of these cells seem to be the main process by which this mutation causes diabetes. The underlying mechanisms and variability in clinical presentation are discussed.     

Molecular mechanisms of mitochondrial diabetes (MIDD)

Mitochondria provide cells with most of the energy in the form of adenosine triphosphate (ATP). Mitochondria are complex organelles encoded both by nuclear and mtDNA. Only a few mitochondrial components are encoded by mtDNA, most of the mt‐proteins are nuclear DNA encoded. Remarkably, the majority of the known mutations leading to a mitochondrial disease have been identified in mtDNA rather than in nuclear DNA. In general, the idea is that these pathogenic mutations in mtDNA affect energy supply leading to a disease state. Remarkably, different mtDNA mutations can associate with distinct disease states, a situation that is difficult to reconcile with the idea that a reduced ATP production is the sole pathogenic factor. This review deals with emerging insight into the mechanism by which the A3243G mutation in the mitochondrial tRNA (Leu, UUR) gene associates with diabetes as major clinical expression. A decrease in glucose‐induced insulin secretion by pancreatic beta‐cells and a premature aging of these cells seem to be the main process by which this mutation causes diabetes. The underlying mechanisms and variability in clinical presentation are discussed.     

Mitochondrial oxidative stress and mitochondrial DNA.

Mitochondria produce reactive oxygen species (ROS) under physiological conditions in association with activity of the respiratory chain in aerobic ATP production. The production of ROS is essentially a function of O2 consumption. Hence, increased mitochondrial activity per se can be an oxidative stress to cells. Furthermore, production of ROS is markedly enhanced in many pathological conditions in which the respiratory chain is impaired. Because mitochondrial DNA, which is essential for execution of normal oxidative phosphorylation, is located in proximity to the ROS-generating respiratory chain, it is more oxidatively damaged than is nuclear DNA. Cumulative damage of mitochondrial DNA is implicated in the aging process and in the progression of such common diseases as diabetes, cancer, and heart failure.     

Mechanisms of mitochondrial diseases

Mitochondria are essential organelles with multiple functions, the most well known being the production of adenosine triphosphate (ATP) through oxidative phosphorylation (OXPHOS). The mitochondrial diseases are defined by impairment of OXPHOS. They are a diverse group of diseases that can present in virtually any tissue in either adults or children. Here we review the main molecular mechanisms of mitochondrial diseases, as presently known. A number of disease-causing genetic defects, either in the nuclear genome or in the mitochondria's own genome, mitochondrial DNA (mtDNA), have been identified. The most classical genetic defect causing mitochondrial disease is a mutation in a gene encoding a structural OXPHOS subunit. However, mitochondrial diseases can also arise through impaired mtDNA maintenance, defects in mitochondrial translation factors, and various more indirect mechanisms. The putative consequences of mitochondrial dysfunction on a cellular level are discussed.     

Mitochondrial DNA and aging

Among the numerous theories that explain the process of aging, the mitochondrial theory of aging has received the most attention. This theory states that electrons leaking from the ETC (electron transfer chain) reduce molecular oxygen to form O2*- (superoxide anion radicals). O2*-, through both enzymic and non-enzymic reactions, can cause the generation of other ROS (reactive oxygen species). The ensuing state of oxidative stress results in damage to ETC components and mtDNA (mitochondrial DNA), thus increasing further the production of ROS. Ultimately, this 'vicious cycle' leads to a physiological decline in function, or aging. This review focuses on recent developments in aging research related to the role played by mtDNA. Both supportive and contradictory evidence is discussed.     

Variations in mitochondrial DNA and gene transcription in freezing-tolerant larvae of Eurosta solidaginis (Diptera: Tephritidae) and Gynaephora groenlandica (Lepidoptera: Lymantriidae)

Respiration, mitochondrial (mt)DNA content, and mitochondrial-specific RNA expression in fat body cells from active and cold-adapted larvae of the goldenrod gall fly, Eurosta solidaginis, and the Arctic woolly bear caterpillar, Gynaephora groenlandica, were compared. Reduced amounts of mtDNA were observed in cold-adapted larvae of both E. solidaginis and G. groenlandica collected in fall or winter, compared with summer-collected larvae. mtDNA increased to levels similar to those of summer-collected larvae after incubation at 10 degrees C or 15 degrees C for 5 h. Mitochondrial-specific RNAs (COI and 16S) were observed in fat body cells of both active and cold-adapted E. solidaginis larvae. Our results suggest that mitochondrial proteins required for respiration may be restored rapidly from stable RNAs present in overwintering larvae.     

Real-time detection and quantification of mitochondrial mutations with oligonucleotide primers containing locked nucleic acid

BACKGROUND: The phenotypic expression of disorders caused by point mutations, deletions or depletions within the mitochondrial genome (mtDNA) is heterogeneous. This relates to the phenomena of heteroplasmy, tissue threshold as well as the distribution of mutant DNA among tissues. Hence, the diagnostics of these disorders demands highly specific, sensitive and quantitative methods. METHODS: We have developed an allele-specific quantitative real-time PCR method for the detection of two of the most prevalent disease causing mitochondrial mutations, m.3243A>G (MELAS) and m.8993T>G (NARP). Locked Nucleic Acid (LNA) modified primers were used to obtain high allele specificity. In order to monitor mtDNA depletion a real-time method for mtDNA/nuclear DNA copy number ratio determination was developed. RESULTS: Rapid and sensitive detection and quantification of MELAS and NARP mtDNA alleles were achieved. Heteroplasmy levels as low as 0.01% could be detected, and the mtDNA/nuclear DNA ratio could be determined. CONCLUSIONS: The present method that allows simultaneous determination of heteroplasmy levels and mtDNA/nuclear DNA copy number ratio, will provide a useful tool in molecular diagnostics and in future epidemiological studies of mitochondrial diseases.     

Curious cases: Altered dose–response relationships in addiction genetics

Dose–response relationships for most addictive substances are “inverted U”-shaped. Addictive substances produce both positive features that include reward, euphoria, anxiolysis, withdrawal-relief, and negative features that include aversion, dysphoria, anxiety and withdrawal symptoms. A simple model differentially associates ascending and descending limbs of dose–response curves with rewarding and aversive influences, respectively. However, Diagnostic and Statistical Manual (DSM) diagnoses of substance dependence fail to incorporate dose–response criteria and don't directly consider balances between euphoric and dysphoric drug effects. Classical genetic studies document substantial heritable influences on DSM substance dependence. Linkage and genome-wide association studies identify modest-sized effects at any locus. Nevertheless, clusters of SNPs within selected genes display 10⁻² > p > 10⁻⁸ associations with dependence in many independent samples. For several of these genes, evidence for cis-regulatory, level-of-expression differences supports the validity of mouse models in which levels of expression are also altered. This review documents surprising, recently defined cases in which convergent evidence from humans and mouse models supports central influences of altered dose–response relationships in mediating the impact of relevant genomic variation on addiction phenotypes. For variation at loci for the α5 nicotinic acetylcholine receptor, cadherin 13, receptor type protein tyrosine phosphatase Δ and neuronal cell adhesion molecule genes, changed dose–response relationships conferred by gene knockouts in mice are accompanied by supporting human data. These observations emphasize desirability of carefully elucidating dose–response relationships for both rewarding and aversive features of abused substances wherever possible. They motivate consideration of individual differences in dose–response relationships in addiction nosology and therapeutics.     

Zidovudine Induces Downregulation of Mitochondrial Deoxynucleoside Kinases: Implications for Mitochondrial Toxicity of Antiviral Nucleoside Analogs

Mitochondrial thymidine kinase 2 (TK2) and deoxyguanosine kinase (dGK) catalyze the initial phosphorylation of deoxynucleosides in the synthesis of the DNA precursors required for mitochondrial DNA (mtDNA) replication and are essential for mitochondrial function. Antiviral nucleosides are known to cause toxic mitochondrial side effects. Here, we examined the effects of 3′-azido-2′,3′-dideoxythymidine (AZT) (zidovudine) on mitochondrial TK2 and dGK levels and found that AZT treatment led to downregulation of mitochondrial TK2 and dGK in U2OS cells, whereas cytosolic deoxycytidine kinase (dCK) and thymidine kinase 1 (TK1) levels were not affected. The AZT effects on mitochondrial TK2 and dGK were similar to those of oxidants (e.g., hydrogen peroxide); therefore, we examined the oxidative effects of AZT. We found a modest increase in cellular reactive oxygen species (ROS) levels in the AZT-treated cells. The addition of uridine to AZT-treated cells reduced ROS levels and protein oxidation and prevented the degradation of mitochondrial TK2 and dGK. In organello studies indicated that the degradation of mitochondrial TK2 and dGK is a mitochondrial event. These results suggest that downregulation of mitochondrial TK2 and dGK may lead to decreased mitochondrial DNA precursor pools and eventually mtDNA depletion, which has significant implications for the regulation of mitochondrial nucleotide biosynthesis and for antiviral therapy using nucleoside analogs.     

Photodynamic and Sonodynamic Treatment by Phthalocyanine on Cancer Cell Lines

Photodynamic therapy is a modality of treatment for tumors. The photochemical interactions of sensitizer, light and molecular oxygen produce reactive oxygen species (ROS) such as singlet oxygen, peroxide, hydroxyl radical and superoxide ion. The tumor is destroyed either by the formation of highly reactive singlet oxygen (type II mechanism) or by the formation of radical products (type 1 mechanism) generated in an energy transfer reaction. The resulting damage to organelles within malignant cells leads to tumor ablation. The cellular effects include membrane damage, mitochondrial damage and DNA damage. A new treatment modality called sonodynamic therapy has been developed, in which the ultrasound–induced cytotoxicity of sonochemical sensitizers inhibits tumor growth. In this study, the promising new generation of sensitizers – phthalocyanines – were used to induce the photodamage. In addition, we applied an ultrasound treatment to support the photodynamic effect. We report on the production of ROS in G361 melanoma cells. Light-emitting diodes were used to evoke the photodynamic effect. Changes in cells were evaluated using fluorescence microscope and atomic force microscopy. The quantitative ROS production changes in relation to sensitizer concentration, irradiation doses and ultrasound intensity were proved by a fluororeader. Our results showed the highest generation of ROS within G361 melanoma cells was achieved at an irradiation dose of 15 Jcm^-2 followed by ultrasound treatment at intensity of 2 Wcm^-2 and frequency of 1 MHz in the presence of 100 μM chloroaluminum phthalocyanine disulfonate (ClAlPcS₂). These results suggest that ClAlPcS₂ is a potential photosensitizer and sonosensitizer for sonodynamic or photodynamic treatment of cancer. (E-mail: kol@tunw.upol.cz)     

Deficient mitochondrial biogenesis in critical illness: cause,effect, or epiphenomenon?

Recent studies indicate that mitochondrial dysfunction plays a role in the pathogenesis of a number of disease states. The importance of these organelles in shock and multiple organ dysfunction is of particular interest to those caring for the critically ill. Mitochondria have their own unique DNA (mtDNA) that encodes 13 essential subunits of electron transport chain enzymes, two ribosomal RNAs and 22 transfer RNAs. Importantly, mtDNA is especially susceptible to deletions, rearrangements and mutations because it is not bound by histones and lacks the extensive repair machinery present in the nucleus. The study by Côté et al. in this issue of Critical Care examines changes in mtDNA in critically ill patients. The results support further investigation into the role of mtDNA in the critically ill.The role of mitochondria in systemic disease has been under-appreciated, and in this issue of Critical Care, Côté et al. [1] examine changes in mitochondrial DNA (mtDNA) in critically ill patients. However, recent evidence has demonstrated impaired oxidative phosphorylation and defective mitochondrial homeostasis in a number of disorders [2,3]. Although the concept of mitochondrial dysfunction and bioenergetic failure during sepsis and shock is not new, recent experimental approaches have yielded novel and interesting findings [4-6]. These have led us and others to propose intriguing hypotheses regarding the pathogenesis of acquired mitochondrial dysfunction in a variety of disease states.In this issue, Côté et al. examine changes in mtDNA in critically ill patients. Their data demonstrate a 30% reduction in the ratio of mtDNA to nuclear DNA (nDNA) in circulating cells of 28 critically ill patients when compared to healthy controls [1]. More importantly, this ratio increased by almost 30% at four days in survivors while non-survivors experienced a further reduction in the mtDNA/nDNA ratio. One might conclude that loss or failed synthesis of mtDNA is a unifying cause of sepsis-induced mitochondrial dysfunction and that clinicians could use mtDNA copy number to predict mortality during critical illness. This requires a more detailed examination of mtDNA heterogeneity and mitochondrial regeneration.Each mitochondrion has 2–10 copies of its own circular genome. These encode for 13 essential subunits of electron transport chain enzymes, two ribosomal RNAs and 22 transfer RNAs [7]. The structural subunits of the electron transport complexes and other mitochondrial proteins arise from nuclear genes [8]. Thus, expression of the genes encoding mitochondrial enzyme complexes is under dual control. mtDNA is particularly prone to deletions, rearrangements and mutations caused by oxidative stress because it is unbound by histones and because these organelles lack the extensive repair systems seen in the nucleus [9]. Therefore, reactive oxygen species produced during oxidative phosphorylation in a variety of disease states can damage mtDNA and mitochondrial proteins. This would lead to decreased ATP production and enhanced programmed cell death [7].Heteroplasmy describes the coexistence of both mutant mtDNA and wild-type, non-mutant mtDNA within the same cell [8]. If the mitochondrial genome drift results in a significant amount of mutant mtDNA, cells exhibit reduced energy capacity and organs become dysfunctional [7]. The threshold for these processes is lower in highly oxidative tissue such as brain, heart, skeletal muscle, retina, kidney and endocrine organs [8]. This threshold effect explains tissue-related variability in the clinical presentation of both inherited and acquired mitochondrial diseases [8].Impaired mitochondrial biogenesis represents an additional manner in which mitochondria may contribute to acquired disorders. Biogenesis includes all of the processes needed for mitochondrial homeostasis and division. It requires precise coordination between both mitochondrial and nuclear-encoded gene products as well as maintenance and replication of mtDNA [10,11]. Recent investigation demonstrates that experimental murine sepsis caused mitochondrial oxidative stress, a loss of mtDNA copy number and depressed basal metabolism in the septic liver [12]. In the recovery phase, mitochondrial biogenesis restored mtDNA copy number and oxidative metabolism.Our understanding of bioenergetic failure in sepsis and shock has been largely limited by interpretation of early investigations. These studies assumed that preservation of cellular ATP indicated intact electron transport [13,14]. However, more recent data make it clear that cells can adapt and maintain viability by down-regulating oxygen consumption, energy requirements and ATP demand [15,16]. In the heart this response is called myocardial hibernation and results in cardiomyocyte hypocontractility with preserved cellular ATP [15]. Hibernating cells maintain ATP levels in the setting of defective oxidative phosphorylation by ceasing nonessential cellular functions to limit ATP utilization [15,16]. At the organ level, this down-regulated metabolic state may manifest as "organ dysfunction" or "organ failure". During hypoxia, ischemia and in early or non-fatal sepsis, such a response appears to be adaptive and often reversible as cells at risk maintain viability and recover after reoxygenation and reperfusion. Our data, however, indicate that during lethal sepsis a similar hibernation response, while initially adaptive, may become problematic as cells remain persistently down-regulated, enzyme complex content and activity decrease and organ failure becomes irreversible [3,4]. This may result from an acquired defect in gene expression and/or functional activity of any of the electron transport enzymes [17]. Our data suggest that persistently impaired mitochondrial gene expression may represent the irreversible defect that leads to organ failure and death.The hypothesis that therapeutically enhancing mitochondrial biogenesis could improve survival is fascinating, especially if defects in mitochondrial replication and mtDNA synthesis also occur in cells of solid organs. Based on recent reports, it is conceivable that stem cells or fibroblasts may be able to restore defective mitochondria in neighboring cells with wild-type mtDNA [18]. Thus, future investigation should focus on increasing and restoring wild-type mtDNA to restore cellular oxidative capacity and organ function in sepsis and shock.What is most exciting is that we are still gaining insight into this billion year old, complex organelle. However, it remains unclear if mitochondrial impairment causes organ dysfunction, is protective against impending organ injury or is an epiphenomenon. The data presented to date have not directly addressed this issue. These questions demand a more exhaustive investigation of the fascinating processes of mitochondrial biogenesis and homeostasis during both health and disease.     

Drosophila melanogaster mitochondrial DNA: completion of the nucleotide sequence and evolutionary comparisons

The nucleotide sequence of the regions flanking the A + T region of Drosophila melanogaster mitochondrial DNA (mtDNA) has been determined. Included are the genes encoding the transfer RNAs for valine, isoleucine, glutamine and methionine, the small ribosomal RNA and the 5'-coding sequences of the large ribosomal RNA and NADH dehydrogenase subunit II. This completes the nucleotide sequence of the D. melanogaster mitochondrial genome. The circular mtDNA of D. melanogaster varies in size among different populations largely due to length differences in the control region (Fauron & Wolstenholme, 1976; Fauron & Wolstenholme, 1980a, b); the mtDNA region we have sequenced, combined with those sequenced by others, yields a composite genome that is 19,517 bp in length as compared to 16,019 bp for the mtDNA of D. yakuba. D. melanogaster mtDNA exhibits an extreme bias in base composition; it comprises 82.2% deoxyadenylate and thymidylate residues as compared to 78.6% in D. yakuba mtDNA. All genes encoded in the mtDNA of both species are in identical locations and orientations. Nucleotide substitution analysis reveals that tRNA and rRNA genes evolve at less than half the rate of protein coding genes.     

Recombinant adeno-associated virus vector-based gene transfer for defects in oxidative metabolism

Defects in oxidative metabolism may be caused by mutations either in nuclear genes or in mitochondrial DNA (mtDNA). We tested the hypothesis that recombinant adeno-associated virus (rAAV) could be used to complement mtDNA mutations. AAV vector constructs were designed to express the reporter gene encoding green fluorescent protein (GFP), fused to a targeting presequence that directed GFP to be translocated into mitochondria. These vectors mediated expression of mitochondrial-localized GFP, as indicated by fluorescence microscopy and electron microscopy, in respiring human embryonic kidney 293 cells and nonrespiring mtDNA-deficient (rho 0) cells. However, when sequences encoding hydrophobic segments of proteins normally encoded by mtDNA were inserted between the presequence and GFP, mitochondrial import failed to occur. In similar experiments, a fusion was created between pyruvate dehydrogenase (PDH) E1 alpha subunit, a nuclear-encoded mitochondrial gene with its own targeting presequence, and GFP. With this construct, expression of GFP was observed in mitochondria in vitro and in vivo. We conclude that the hydrophobicity of mtDNA-encoded proteins limits their ability to be transported from the cytoplasm. However, rAAV-based gene therapy may hold promise for gene therapy of PDH deficiency, the most common biochemically proven cause of congenital lactic acidosis.     

Oxidative stress,mitochondrial dysfunction and neurodegenerative diseases; a mechanistic insight

Mitochondria is one of the main source of oxidative stress (ROS), as it utilizes the oxygen for the energy production. ROS and RNS are normally generated by tightly regulated enzymes. Excessive stimulation of NAD(P)H and electron transport chain leads to the overproduction of ROS, results in oxidative stress, which is a good mediator to injure the cell structures, lipids, proteins, and DNA. Various oxidative events implicated in many diseases due to oxidative stress include alteration in mitochondrial proteins, mitochondrial lipids and mitochondrial DNA, Which in turn leads to the damage to nerve cell as they are metabolically very active. ROS/RNS at moderate concentrations also play roles in normal physiology of many processes like signaling pathways, induction of mitogenic response and in defense against infectious pathogens. Oxidative stress has been considered to be the main cause in the etiology of many diseases, which includes Parkinson’s and Alzheimer diseases. Several PD associated genes have been found to be involved in mitochondrial function, dynamics and morphology as well. This review includes source of free radical generation, chemistry and biochemistry of ROS/RNS and mitochondrial dysfunction and the mechanism involved in neurodegenerative diseases.     

Quantification of mitochondrial DNA deletion,depletion, and overreplication: application to diagnosis

BACKGROUND: Many mitochondrial pathologies are quantitative disorders related to tissue-specific deletion, depletion, or overreplication of mitochondrial DNA (mtDNA). We developed an assay for the determination of mtDNA copy number by real-time quantitative PCR for the molecular diagnosis of such alterations. METHODS: To determine altered mtDNA copy number in muscle from nine patients with single or multiple mtDNA deletions, we generated calibration curves from serial dilutions of cloned mtDNA probes specific to four different mitochondrial genes encoding either ribosomal (16S) or messenger (ND2, ND5, and ATPase6) RNAs, localized in different regions of the mtDNA sequence. This method was compared with quantification of radioactive signals from Southern-blot analysis. We also determined the mitochondrial-to-nuclear DNA ratio in muscle, liver, and cultured fibroblasts from a patient with mtDNA depletion and in liver from two patients with mtDNA overreplication. RESULTS: Both methods quantified 5-76% of deleted mtDNA in muscle, 59-97% of mtDNA depletion in the tissues, and 1.7- to 4.1-fold mtDNA overreplication in liver. The data obtained were concordant, with a linear correlation coefficient (r(2)) between the two methods of 0.94, and indicated that quantitative PCR has a higher sensitivity than Southern-blot analysis. CONCLUSIONS: Real-time quantitative PCR can determine the copy number of either deleted or full-length mtDNA in patients with mitochondrial diseases and has advantages over classic Southern-blot analysis.     

Antitumor effect of N-succinyl-chitosan nanoparticles on K562 cells

Polymer nanoparticles have become attractive for its prominent property recent years. In this paper, antitumor effects of N-succinyl-chitosan nanoparticles (NSCNP), a nanoparticles derivated from chitosan, were evaluated in K562 cells, including cell viability comparison, cell morphology analysis, DNA fragmentation detection, cell surface potential and mitochondrial membrane potential (MMP) measurement, intracellular ROS and Ca²⁺ concentration evaluation. Our results revealed NSCNP could inhibit the proliferation of K562 with an IC₅₀ of 14.26 μg/ml (24 h); decrease the zeta potential; disrupt the mitochondrial membrane potential; increase ROS generation and Ca²⁺ concentration. Cytomorphology study and DNA fragment analysis reveal characteristics of apoptosis and necrosis, indicating that the antitumor effect of NSCNP achieved by necrosis and apoptosis induction in K562 cells.     

The CO/HO system reverses inhibition of mitochondrial biogenesis and prevents murine doxorubicin cardiomyopathy

The clinical utility of anthracycline anticancer agents, especially doxorubicin, is limited by a progressive toxic cardiomyopathy linked to mitochondrial damage and cardiomyocyte apoptosis. Here we demonstrate that the post-doxorubicin mouse heart fails to upregulate the nuclear program for mitochondrial biogenesis and its associated intrinsic antiapoptosis proteins, leading to severe mitochondrial DNA (mtDNA) depletion, sarcomere destruction, apoptosis, necrosis, and excessive wall stress and fibrosis. Furthermore, we exploited recent evidence that mitochondrial biogenesis is regulated by the CO/heme oxygenase (CO/HO) system to ameliorate doxorubicin cardiomyopathy in mice. We found that the myocardial pathology was averted by periodic CO inhalation, which restored mitochondrial biogenesis and circumvented intrinsic apoptosis through caspase-3 and apoptosis-inducing factor. Moreover, CO simultaneously reversed doxorubicin-induced loss of DNA binding by GATA-4 and restored critical sarcomeric proteins. In isolated rat cardiac cells, HO-1 enzyme overexpression prevented doxorubicin-induced mtDNA depletion and apoptosis via activation of Akt1/PKB and guanylate cyclase, while HO-1 gene silencing exacerbated doxorubicin-induced mtDNA depletion and apoptosis. Thus doxorubicin disrupts cardiac mitochondrial biogenesis, which promotes intrinsic apoptosis, while CO/HO promotes mitochondrial biogenesis and opposes apoptosis, forestalling fibrosis and cardiomyopathy. These findings imply that the therapeutic index of anthracycline cancer chemotherapeutics can be improved by the protection of cardiac mitochondrial biogenesis.